Congrats on taking the next step to reaching a healthier you by getting active with SparkPeople - it's a great community, wonderful resources and fantastic support. You're off to a great start already by getting a medical checkup and then posting here!
I know others are stating absolutely that a 900 calorie diet is not healthy but I do not believe that is always true because it's an individual thing - not knowing anything else about you, none of us is really qualified to say it is or is not healthy because what is best for someone who is very petite is not going to be the same for someone who is very large - with that said, however, my personal experience is that very few doctors have any idea at all about nutrition or how to lose weight. They do not receive that training in ordinary med school and as a group, they are probably no better of a source for information than anyone else on the street.
Obviously there are going to be exceptions - some doctors, like some 'people on the street,' really do have a great deal of knowledge about nutrition, health and weight loss. Others, doctors and most people who are not dietitians, nutritionists or other specialists, are subject to influences that may not be very good sources of information.
So - I do suggest that you make sure the target number of calories is REALLY right for you. There are basic 'suggested base numbers' that can be adjusted up or down according to your age, gender, weight, height, medical conditions, medications, body composition and activity level. Someone who is physically super active burns more calories than someone who lives a sedentary life [duh!!] - and there are many other things that influence what is right for you.
I will suggest that you start by having your RMR [aka base metabolism] measured so you know how many calories you burn to keep your body functions going. Once you find out your base metabolism, you might want a second test to find out how many calories you burn with various heart rates associated with activities. Then take those numbers to an experienced nutritionist or dietitian who specializes in bariatrics or weight loss for a customized program.
If you don't want to [or can't] spend the money for these, then use a knowledgeable site such as this one to get guidelines - use the SparkPeople tools to generate a meal plan for you with the proper number of calories they recommend for you. If you follow the plan and get the right amount of exercise they suggest to go along with it but don't see results after a couple of months, then you might need to get the individualized testing and plan anyway.
After many years of struggling with my weight, I had the tests done myself. I discovered my metabolism happens to be super-slow and I also don't burn as many calories during activity as would be expected from most people my age, etc. I did work with a nutritionist/personal trainer who also works with several doctors and bariatric programs. She helped me develop target calorie ranges and gave me sample meals and eating guidelines to follow, along with exercise targets and they are different from what any generalized program comes up with for me because these are based on my actual numbers instead of the 'typical' or 'expected' numbers.
So as it happens, my target calorie range is lower than most people here on SP consider 'healthy' - however, like other SP members, I also worry about people who just throw numbers around and suggest 500 calories, 900 calories or whatever without having the necessary ACTUAL information to support the suggestion but for me, 900 to 1200 calories is the proper target level, while for most people my size, age, etc, the range would probably be 1200-1600 calories. I would NEVER EVER suggest someone go on a 900 calorie diet without getting medical monitoring, which I do get, and without having a very knowledgeable person oversee your program, which I also have.
Aside from all this, I suggest you check out the SparkTeams - I think you will find a lot of others 'just like you' including many with the same challenges, circumstances and goals. You can choose SparkTeams by age group, lifestyle or interests, geographic location or several other ways.
Some of the teams I like and think you might like include the Official 10-minute Daily Exercise Streak Challenge, Starting Over Weekly Mini-Challenge Team, 10k Steps A Day and Motivation & Positive Attitude Plan - but there are so many to choose from, you can have a great time looking for the ones that seem to fit you best! In fact, I suggest joining more than one group, post your intro there and write blogs as often as you can - you will find tons of friends and support that way, I promise!!
In my experience, SparkPeople is like a
in some ways - it's lots of fun and easy to make friends because we're all in this together. I like the way a HEALTHY LIFESTYLE is emphasized instead of a 'quick fix wonder diet' so it's good for people wanting to lose weight, maintain a previous loss, get healthier, improve fitness and many other goals including gaining weight or saving money - it's about waaaaaay more than 'just' losing weight so you have definitely come to the right place!
If you ever need any help using features of the site, there are tutorial videos under the HELP section that can show you how to use the features of the site. You can also find them on the START page and several other places on the site.
Be sure to read and 'study' The Spark book because it outlines the overall program and is compatible with most types of eating plans. Right now there is a 'special offer' on Amazon to get it in electronic format for just $1.99 - you can download the free Kindle reader for your computer or read it on a smartphone so you don't have to actually own a Kindle device to take advantage of this generous offer - so check it out!!!
If you haven't already discovered the SparkDiet linked at the bottom of the START page, check it out - the program is simple but extremely effective. There is a TON of information on this site - so much it might even seem overwhelming but fortunately we don't have to 'digest' everything at once! The FastBreak program is a good way to start.
Another nice thing about SparkPeople is that we have permission to be human - we don't have to change everything at once or be in a hurry to reach our goals. Take a few baby steps and then a few more and before you know it, you'll have completed a long journey - I hope you enjoy this community as much as I have - it teaches us how to make positive lifetime changes because that's the only thing that will work over time!